A tappet of the pre-cited type is disclosed in the generic document DE 100 02 287 A1. This tappet likewise comprises on one of its front ends, two cheek-like extensions situated diametrically opposite each other. A roller for making contact with a cam is mounted for rotation on an axle that extends between the extensions. These extensions are left over, so to speak as “residual parts” after a milling operation (disk milling) for example, and thus form axial extensions of the housing.
In addition, a person skilled in the art will see that an inner element is installed in the pre-cited tappet for axial movement relative to its housing and comprises a hydraulic lash adjuster, and that a piston-like coupling means is arranged in the inner element for an optional coupling of the inner element to the housing. The lash adjuster and the coupling means are pressurized with hydraulic medium through separate passages leading to a guide bore (not illustrated) of the roller tappet. As a rule, these passages are situated precisely on the axially shorter side of the periphery of the housing, that is to say, on the side that is offset at 90° to the cheek-like extensions.
A particular drawback of this design is that, precisely in this peripheral region, only a short axial sealing length is available. This means, in other words, that due to the short axial leak gap formed between the outer peripheral surface of the housing and the guide bore, unnecessarily high hydraulic medium losses are to be expected. In the worst case, it is also possible for a lower front end of the tappet to penetrate into edge regions of the lower passage.
It is true that closed “spaces” for the roller on the tappet are known from prior art documents, for instance, from DE 199 15 531 A. However, this closed design has a number of inherent drawbacks. On the one hand, the total mass of the tappet is unnecessarily increased and this has a detrimental effect on the oscillating mass of the valve train. On the other hand, it is only with considerable difficulty that the closed roller pocket can be fabricated, and as can be seen from the cited prior art, it has to be connected to the rest of the tappet body by an appropriate, complicated and cost-intensive connecting or joining method. The fact that an adequate lateral freedom of movement of the roller relative to the wall of its pocket is still required restricts the possibilities of its designing and arrangement.